Once we involved in one particular relationship, it is impossible to keep same relation where it is started.
I think with in long term relationship we have series of short term-relationship. Ever wonder about those short term-relationship? May be that state of short term relationship may be small with larger context of relationship, but it redefines our original relationship. No wonder we see friends becoming best friends, lovers getting married, from group of people emerging leader, small quarrel leading to killing of friend.
Benchmark for any relationship is how it gets evolved over time . But what changes over the time, which causes relationship to change? Is it surrounding of people, status of people, time committed to relation or it just comes down to interpersonal communication skills?